If I am understanding your question correctly, use a sheet of paper or cardboard to make an exact copy of you firewall....dimensions and shape. Once you have accurately cut the template from the paper, lay it on the firewall and copy your crosshair lines, or measure them and draw them on the paper. Mark your mounting holes from the motor to the paper. Accurately tape the template with the mounting hole marks onto the firewall and drill your holes. Am I interpreting your question correctly?